Usually the MX
2
intelligent Wye to Delta transition algorithm provides an optimal transition point that minimizes the transient current
and torque surges that can occur. However, the Wye to Delta transition will occur when the Up To Speed Time parameter has expired.
In order to reduce the current surge during the transition from Wye to Delta mode, the Up To Speed Time parameter should be adjusted
so that the transition occurs as close to full speed as possible within the constraints of the load. If the Up To Speed Time is set too short,
the starter will transition too soon and a large current and torque surge will occur. If the Up To Speed Time is set too long, the motor
may not have sufficient torque to continue accelerating when in Wye mode and may stop accelerating at a low speed until the transition
to Delta mode occurs. If this occurs, the start is unnecessarily prolonged and motor heating is increased.
A typical closed transition Wye-Delta starting current profile is shown in Figure 42.
A digital input can be programmed as a 2M contactor feedback input. This input provides verification that the 2M contactor has fully
closed preventing operation when the transition resistors are still connected in the motor circuit. The use of this feedback is
recommended to prevent the overheating of the transition resistors if the 2M contactor does not close properly. The 2M confirmation trip
time can be adjusted by modifying the Bypass Feedback Time parameter.
z NOTE: When in Wye-Delta mode, the acceleration ramp, kick, and deceleration settings have no effect on motor operation.
z NOTE: When in Wye-Delta mode, the SCR gate outputs are disabled.
162
7 - THEORY OF OPERATION
100%
200%
300%
400%
500%
600%
0%
100%
% speed
Wye-Delta Closed Transition Current Profile
% Full
Load
Motor
Current
Transition from Wye to Delta mode
Figure 42: Wye Delta Profile
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